Does anyone know how to allow for a group mailbox to be set as the access request recipient in SharePoint Online? I am receiving an invalid email address message but the email is valid. I am not finding much on this topic online.
It looks like there is a method behind the scenes that blocks the 'onmicrosoft.com' domain from being added. Verify you're using an email address assigned to the Office 365 Group that is not using 'onmicrosoft.com' in the alias.
Shared Mailboxes will not work as they cannot be resolved by SharePoint. Distribution Lists also cannot be resolved and you'll run into the same error.